In the field of imaging, document files can include vector graphic elements which represent the intended appearance of a document. Some documents include graphic elements that overlap such that the overlapping colors combine to produce a different color.
The related applications identified in the cross reference disclose a few techniques for altering an original document to handle problems that can occur when overlapping graphic elements include elements that are configured to overprint. One exemplary problem is the incorrect rendering of intended color when the document is color matched. In particular, color matching can result in a change in the set of colors printed by an element so that when rendered, significant color shifts can occur in areas where overprinting elements overlap. As an example, a process color, painted by a background element in an area where a spot color overprints and overlaps, will no longer contribute to the area if color matching converts the spot color to a process recipe that paints that process color of the background. As another example, an overprinting element painting in one or more process color channels may paint in additional channels after color matching and thus prevent background color in the additional channels from contributing color in areas of overlap.
Commonly-assigned U.S. patent application Ser. No. 11/122,090 discloses converting a document by retaining original elements while adding a graphic element to the document to represent the combined color of elements that overlap in an area. While this approach produced the desired results, there is more complexity than desired (e.g. calculating the overlapped overprint areas, determining an appropriate element representation for the area and combining colors from the overlapping elements).
Commonly-assigned U.S. patent application Ser. No. 11/880,330 discloses converting a document by replacing certain graphic elements with new elements that are based on the original elements but with altered graphic attributes including transparency attributes. Although the approaches in U.S. patent application Ser. No. 11/880,330 can be less complex than those of the first related application, the size of the converted document can increase significantly because two or more replacement elements may be produced for each original element to achieve the desired results. Larger files take more resources to store and process (e.g. render). This is particularly acute when spot colorants are used.
Thus, there is still a need to have a document conversion approach that produces the desired results, is relatively simple and does not incur a large increase in the number of graphic elements.